Multi-stage transmission devices having a multi-gear transmission mechanism (for example, 4 to 8 forward stages, and 1 to 2 reverse stages) in which the transmission gear ratio cannot be continuously adjusted during operation have been conventionally used as an automatic transmission (AT) for a vehicle. As this kind of multi-stage transmission, a transmission having a torque converter and planetary gear mechanism (typical torque converter AT), or an automated manual transmission (AMT) that automatically performs shifting operation (shift down, shift up) and clutch disconnecting/connecting operation of a multi-stage (manual) transmission by way of a hydraulic or an electric actuator that is controlled by a controller are known.
Moreover, the use of continuously variable transmissions (CVT) capable of continuously adjusting the transmission gear ratio, such as a belt continuously variable transmission and toroidal continuously variable transmission, have increased in recent years. Furthermore, infinitely variable transmissions (IVT), which are a combination of a continuously variable transmission such as toroidal continuously variable transmission and a differential gear mechanism (for example, a planetary-gear transmission), the transmission path of which can be freely switched by a clutch mechanism, and that make it possible to have an infinitely large transmission gear ratio, are also known. In a vehicle in which this kind of multi-stage transmission device or continuously variable transmission device is assembled, transmission control is performed in order to perform adjustment to the most optimum gear stage or transmission gear ratio (target gear stage, target transmission gear ratio) depending on the traveling state at that instant that is obtained from the accelerator pedal operation (accelerator opening) or the traveling speed of the vehicle (vehicle speed), and lock-up-clutch control of a torque converter, and necessary connecting/disconnecting control of the clutch is performed.
Incidentally, when driving a vehicle in which this kind of automatic transmission is installed, due to erroneous operation or intentional operation (knowingly performed) by the driver, the shift lever may be shifted to a selection position for a direction opposite the traveling direction of the vehicle at that instant. In other words, when the selection position of the shift lever is in the D range (normal forward position) or L range (high drive forward position), and the vehicle is traveling in the forward direction, the shift lever may be shifted and set in the R range (reverse position), or, on the other hand, when the selection position of the shift lever is in the R range and the vehicle is traveling in the reverse direction, the shift lever may be shifted and set in the D range or L range. Of this kind of operation, intentional (knowingly performed) operation by the driver is performed such as when putting the vehicle into a garage. In other words, when putting a vehicle into a garage, without the vehicle being in a completely stopped state, the shift lever may be shifted (garage shifting) from the “D range→N range→R range while traveling forward” or may be shifted from the “R range→N range→D range when traveling backward”.
In an industrial vehicle such as a farm vehicle or construction vehicle, switching between forward and reverse is performed frequently during work, however, this kind of switching between directions may be performed by shifting the shift lever (shuttle shifting) to a selection position for a direction opposite the traveling direction of the vehicle at that instant. In that case, together with adjusting to the gear stage or transmission gear ratio that corresponds to the position where the shift lever is shifted to (shift position), and the clutch corresponding to that shift position is connected, the behavior of the vehicle changes suddenly such as sudden deceleration, tire lock, engine stall or the like, and when this change is severe, there is a possibility that damage to the vehicle or transmission device will occur such as breakage of the propeller shaft, damage to the inside of the transmission device, clutch burst or the like.
In consideration of such a situation, JP 2007-309435 (A) discloses technology that, in a continuously variable device that is a combination of a toroidal continuously variable transmission and a planetary gear transmission as described above, when the shift lever is shifted to a selection position for a direction opposite the traveling direction of the vehicle at that time, prevents sudden change in the behavior of the vehicle, and prevents damage to the vehicle and transmission device. More specifically, JP 2007-309435 (A) discloses technology that, when the shift lever is shifted to a selection position for a direction opposite the traveling direction of the vehicle at that time, keeps the speed ratio of the continuously variable transmission device at a value that corresponds to the traveling state at that time, and connects the clutch device, then adjusts the speed ratio to a value that makes it possible to achieve a stopped state of the vehicle.
However, in the continuously variable transmission disclosed in JP 2007-309435 (A), with the shift lever shifted to a selection position for a direction opposite the traveling direction of the vehicle at that time, releasing the connection of the clutch device is not taken into consideration. For example, in the case of industrial vehicles such as farm vehicles or construction vehicles, with the shift lever shifted to the direction opposite the traveling direction at that time, the operator may step on the accelerator pedal with the intention of traveling in the opposite direction as quickly as possible, or with the intention of accelerating in that opposite direction. Such operation (shuttle shifting) is performed frequently by the operator with the intention of quickly stopping the vehicle and quickly accelerating in the opposite direction. When this kind of operation is performed, in the continuously variable transmission device that is disclosed in JP 2007-309435 (A), the clutch device remains connected regardless of the traveling speed of the vehicle, so there is a possibility that the vehicle will continue to travel at high speed for a short time in the direction opposite the selected direction of the shift lever (direction opposite the direction intended by the operator). Therefore, it is not possible to achieve the behavior intended by the operator (quick stopping and acceleration), and there is a possibility that this will bring about a decrease in work efficiency. Moreover, this kind of vehicle behavior that differs from the intention of the operator gives an uncomfortable feeling to the operator, and is not preferable.
JP 2004-190809 (A) discloses technology in which, in order to prevent sliding between the belt and pulley in a belt continuously variable transmission when starting to move, the connection of a forward clutch and a reverse clutch is made smooth by adjusting the hydraulic pressure that is introduced into these clutches by a garage shifting control valve that is connected to the shift lever. Moreover, JP 3,924,164 (B2) discloses technology that prevents slipping between the belt and pulley in a belt continuously variable transmission by suitably regulating the force for holding the belt by the pulley by a garage shifting control valve when the shift lever is shifted to a selection position for the direction opposite the traveling direction of the vehicle at that time. However, in the continuously variable transmissions disclosed in this literature, the number of parts increases by providing a garage shifting control valve, as well as construction and control becomes more complicated, so there is a possibility that maintaining reliability will become troublesome.
JP 2006-300268 (A) and JP 2007-187288 (A) disclose technology in which a continuously variable transmission device that is used in construction vehicles or farm vehicles, and has modes in which the rotating state of the output shaft is switched between a forward state and reverse state that are on both sides of a so-called geared neutral (GN) state in which the rotating state of the output shaft is stopped while the input shaft continues to rotate in one direction. JP 2006-300268 (A) discloses technology in which the fluctuation range (transmission range) of the speed ratio on the forward side and on the reverse side is increased by providing a forward/reverse switching mechanism in such a continuously variable transmission device that is capable of achieving this kind of geared neutral state. Moreover, JP 2007-187288 (A) discloses technology that gradually increases the transmission gear ratio of a toroidal continuously variable transmission in order to travel in the direction corresponding to the operation direction of the forward/reverse switching lever. However, in the case of continuously variable transmission devices disclosed in the literature above, shifting the shift lever to a selection position for the direction opposite the traveling direction of the vehicle at that time (shuttle shifting) is not considered. Therefore, when this kind of operation is performed, there is a possibility that behavior (quick stopping and acceleration) will not be achieved as intended by the operator.